Effect of Control Mode and Test Rate on the Measured Fracture Toughness of Advanced CeramicsThe effects of control mode and test rate on the measured fracture toughness of ceramics were evaluated by using chevron-notched flexure specimens in accordance with ASTM C1421. The use of stroke control gave consistent results with about 2% (statistically insignificant) variation in measured fracture toughness for a very wide range of rates (0.005 to 0.5 mm/min). Use of strain or crack mouth opening displacement (CMOD) control gave approx. 5% (statistically significant) variation over a very wide range of rates (1 to 80 μm/m/s), with the measurements being a function of rate. However, the rate effect was eliminated by use of dry nitrogen, implying a stress corrosion effect rather than a stability effect. With the use of a nitrogen environment during strain controlled tests, fracture toughness values were within about 1% over a wide range of rates (1 to 80 micons/m/s). CMOD or strain control did allow stable crack extension well past maximum force, and thus is preferred for energy calculations. The effort is being used to confirm recommendations in ASTM Test Method C1421 on fracture toughness measurement.
Document ID
20180002073
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
Hausmann, Bronson D. (Case Western Reserve Univ. Cleveland, OH, United States)
Salem, Jonathan A. (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
March 23, 2018
Publication Date
January 21, 2018
Subject Category
Chemistry And Materials (General)
Report/Patent Number
GRC-E-DAA-TN51799
Meeting Information
Meeting: International Conference and Expo on Advanced Ceramics and Composites